This program involves the investigation of the effects of accelerated heavy charged particles (such as neon and argon ions) on biological material. The research is intended to provide information on the fundamental nature of the interaction of ionizing radiations with biological matter, and on the possible use of such heavy ions in treatment of human cancer. The principal accelerator facility used is the Bevalac, a unique machine capable of producing biomedically useful heavy-ion beams to 1 or 2 GeV/nucleon kinetic energy. Cellular and molecular studies include the effects on survival of mammalian cells in tissue culture; the modification of these effects by oxygen and by pharmacological radiosensitizers and protectors; and the yield of single- and double-strand scission in DNA and its repair. Tissue radiobiology encompasses an initial study of the effects of heavy-ion beams on normal mammalian tissues. Both acute and chronic effects will be considered because they relate to eventual application of the beams to human therapy. Tumor radiobiology is concerned with the kinetics of cell proliferation in animals that receive therapeutic doses. Pretherapeutic physics will make preparations for human applications, including construction of a computerized beam delivery system. This is a core program, and it is the center of several satellite investigations dealing with special aspects of the same subject.